Recently, with the increase of importance of a bin-functional image, importance of PET (Positron Emission Tomography) is greatly increasing. However, the PET has a limit that it is basically difficult to lower the resolution below a half (d/2) of the width (d) of a detector. This will be described with reference to FIG. 1.
According to the PET, if a positron is emitted from a specific pixel, two destroyed photons of 511 KeV are generated and proceed, being separated from each other at an angle of 180 degrees, and are detected by two detectors which stand opposite to each other. The probability that the positron emission in a specific pixel is detected on a response curve that is composed of two specific detectors is called CRF (Coincidence Response Function).
As illustrated as (1) of FIG. 1, an ideal point detector corresponds to a point, and as illustrated as (2) and (3) of FIG. 1, an ideal line of response (LOR) corresponds to an ideal line.
However, a detector of finite extent has a width (d) due to its constant volume as illustrated as (2) and (3) of FIG. 1, and the line of response is not an ideal line as illustrated as (2) of FIG. 1, but has a geometrical CRF as illustrated as (3) of FIG. 1.
(3) of FIG. 1 illustrates the CRF in consideration of only geometrical elements except for other physical variables. Red color indicates high detection probability, and blue color indicates low detection probability. By the geometrical analysis as illustrated in FIG. 1, it is not possible to obtain the resolution that is lower than a half (d/2) of the width of the detector.
Further, as the size of the detector becomes smaller, the sensitivity of the system is greatly degraded, and there is a limit in obtaining a high resolution image.
To overcome this, a fusion imaging system such as PET-CT or PET-MR has been introduced. However, the performance of the PET itself is limited, and this exerts an influence on the fusion imaging system.
The related art related to this issue may be examined as follows.
KR 10-2011-0121536 A discloses a method for obtaining a high resolution image, which moves a PET detector itself or a bed, measures the degree of motion and detects an image signal that is differently detected depending on the motion, and reconstructs a corresponding PSF. However, according to this related art, the high resolution image is not acquired using a plurality of low resolution images, but is acquired through preprocessing or post-processing of the image.
KR 10-2011-0121535 A, JP 2001-330671 A, and U.S. Pat. No. 8,103,487 B disclose methods to improve resolution by reconstructing images without movement of a PET detector itself or a bed.
(Patent Document 1) KR 10-2011-0121536 A
(Patent Document 2) KR 10-2011-0121535 A
(Patent Document 3) JP 2001-330671 A
(Patent Document 4) U.S. Pat. No. 8,103,487 B